asus-wmi: control wlan-led only if wapf == 4

Controlling the wlan led seems to have some side effects to the machines
with wapf value is not equal to 4. It will make the keyboard backlight
out of order.
So, the patch will enable the wlan led function only if the wapf == 4.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=46791



Reported-by: Mirto Silvio Busico <m.busico@ieee.org>
Tested-by: Karol Herbst <karolherbst@me.com>
Tested-by: drunkenbatman <drunkenbatman@gmail.com>
Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>